1. Field of the Invention
The present invention relates to an ionic compound, an electrolytic solution using the same, and an electrochemical device and a battery using the same.
2. Description of the Related Art
Ionic compounds have been widely used hitherto in various fields. As an example, in the field of electrochemical devices, with emphasis on solubility, ionic dissociation and the like, an ionic compound including an anion such as PF6− or BF4− is used as an electrolyte salt.
In the electrochemical devices, in the field of batteries mainly used as power sources for electronic devices, specifically chargeable/dischargeable secondary batteries, research and development aimed at improving battery characteristics such as capacity characteristics or cycle characteristics have been actively conducted. Among them, secondary batteries using insertion and extraction of lithium ions for charge-discharge reaction (that is, so-called lithium-ion secondary batteries), secondary batteries using precipitation and dissolution of lithium metal (that is, so-called lithium metal secondary batteries) can obtain a large energy density, compared to lead-acid batteries or nickel-cadmium batteries in related arts, so they hold great promise.
In secondary batteries of this kind, with emphasis of a conductive property, potential stability and the like, an electrolytic solution formed by dissolving an electrolyte salt such as LiPF6 in a carbonate-based nonaqueous solvent such as propylene carbonate or diethyl carbonate is widely used. As the electrolyte salt, LiBF4, LiCF3SO3, LiClO4, LiAsF6, LiN(CF3SO2)2, LiN(C2F5SO2)2, LiN(C4F9SO2)(CF3SO2) and the like are used in addition to LiPF6. Moreover, recently, bis[oxalate-O,O′] lithium borate, difluoro[oxalate-O,O′] lithium borate or the like is used. The use of difluoro[oxalate-O,O′] lithium borate in the field of electrochemical devices has been proposed to improve heat resistance, hydrolysis resistance and the like (for example, refer to Japanese Unexamined Patent Application Publication No. 2002-110235).